Multiuser/multitasking operating systems such as Unix/Linux/BSD, but also contemporary versions of Windows and the MacOS, provide complex security mechanisms to ensure that normal users can neither mess with the system configuration, nor crash or reboot the computer. However, unless special precautions were made by the system administrator, most of these operating system can be crashed or at least brought to a grinding halt even by unprivileged users by running an insane, ever-growing amount of programs/processes eating up all memory and CPU cycles. The easiest way to achieve this is a "forkbomb", a little program which does nothing but launch two or more copies of itself upon startup, thus setting off a chain reaction with an exponentially growing number of processes. To write forkbombs has been popular entertainment among hackers since about the mid-1990s; in 2002 a forkbomb written in Perl by read_me expert Alex McLean was awarded the software art prize of the transmediale festival in Berlin.
Jaromil, an Italian hacker, political activist and author of the Free Software programs "muse" (a streaming server), "hasciicam" (ASCII art webcam software) and "FreeJ" (a realtime video mixing/manipulation program) is a believer in a concept of software art as beautiful code and high craftsmanship of programming. His forkbomb, which runs on any Unix-like system with a standard Bourne-compatible shell (such as bash or zsh), consists only of the following 13 characters:

:(){ :|:& };:

In other words, if you have access to the terminal prompt of a Unix-like OS, these 14 characters - which look like IRC smilies or chaotic code art - spell a cast that brings it down. Using a terse, abbreviated shell scripting syntax as opposed to other forkbombs which need several lines of sourcecode to achieve the same goal, jaromil's one-liner is arguably the most elegant and efficient forkbomb ever written. It has the potential of becoming a secret code of recognition among the initiated, like the stuffed trumpet of the Tristero underground in Thomas Pynchon's "Crying of Lot 49", or it could even become a popular culture icon to be reprinted on t-shirts, like the ASCII art of Linda Lovelace's blowjob as it was made a net.art icon by the ASCII Art Ensemble.